Proximal reabsorption with changing tubular fluid inflow in rat nephrons

Abstract

SUMMARYThe relative contribution of intraluminal versus peritubular factors in mediating glomerulo-tubular balance (GTB) is still controversial. We modulated the load of tubular fluid to the proximal tubule of single nephrons of rats by injecting oil into the efferent arteries (EAO). In fifty nephrons the changes in reabsorption induced by obstruction occurred in the same direction as, and were significantly correlated with, the simultaneous changes in single nephron glomerular filtration rate (SNGFR) (y = -0-54 + 0-92x, R = 0-91, P < 0-0001). In an additional set of thirty-nine nephrons the load of tubular fluid was changed, during EAO, by partial collection from Bowman's space or from the early proximal convolution. Thus, the rate of tubular fluid delivery along the proximal tubule was changed in an experimental situation that prevented any modification in the oncotic pressure of peritubular capillaries. The changes in proximal deliveries during this experimental condition were significantly correlated with those during reabsorption (y = -2-87 + 0-7 lx, R = 0-82, P < 0.0001). These data demonstrate that GTB is fully expressed even when the native peritubular environment is kept constant while the rate of perfusion of proximal tubular segments with native tubular fluid is changed.

Semi-mechanistic kidney model incorporating physiologically-relevant fluid reabsorption and transporter-mediated renal reabsorption: pharmacokinetics of γ-hydroxybutyric acid and l-lactate in rats

“…Theoretical, experimental, and mathematical aspects of renal clearance [20]. and effects of interplay of intrinsic and extrinsic factors [21], such as plasma protein binding [22], urine flow [23–25], urine pH [23], and osmotic diuresis [26], on the renal clearance of drugs have been extensively reported. Studies of nephron physiology have elucidated mechanisms of solute and water transport in proximal tubules [27–29], and described mathematical systems models of the urine concentrating mechanism in the rat renal medulla [30,31], and mathematical models of rat proximal tubule, loop of Henle and collecting ducts [32–34].…”

Flow-dependent transport in a mathematical model of rat proximal tubule

“…Perhaps the most important luminal factor is a direct effect of axial flow velocity on reabsorption (32,56), and along with its impact on sodium reabsorption, luminal flow has been found to influence the transport of glucose (22), bicarbonate (1,8,25), and chloride (15,57). Insight into the mechanism underlying flow-dependent transport came with the demonstration that increases in axial flow velocity recruit new Na ϩ /H ϩ transporters into the luminal membrane (26,30).…”

Modeling Proximal Tubule Cell Homeostasis: Tracking Changes in Luminal Flow

“…This "glomerulotubular balance" derives from both peritubular capillary and luminal factors (Gertz and Boylan, 1973; Haberle and von Baeyer, 1983; Weinstein, 1990). The most important luminal factor is a direct effect of axial flow velocity on transport (Wilcox and Baylis, 1985; Romano et al, 1998), and along with its impact on sodium reabsorption, luminal flow has been found to influence the transport of glucose (Knight et al, 1980), bicarbonate (Chan et al, 1982; Alpern et al, 1983; Liu and Cogan, 1988), and chloride (Green et al, 1981; Wong et al, 1995). Insight into the mechanism underlying flow-dependent transport came with the demonstration that increases in axial flow velocity recruit new Na + /H + transporters into the luminal membrane (Preisig, 1992; Maddox et al, 1992).…”